Bluetooth Low Energy (BLE) relates to Bluetooth wireless radio technology. It has been designed for low-power and low latency applications for wireless devices within short range. Today, BLE applications can be found from healthcare, fitness, security, smart energy, industrial automation and home entertainment. However, BLE is not limited only those, but increasingly more new application utilizing BLE technology are designed.
The difference between BLE and classic Bluetooth is that the BLE devices consume remarkably less power for communication than classic Bluetooth devices. In addition, the BLE is able to start the data transmission much quicker than the classic Bluetooth. This makes it possible to have BLE devices constantly on and to communicate intermittently with other devices.
In BLE technology, one or more so called slave devices can be connected to a master device. To let the master know about the slave devices before connection, the slave devices (or at that point “advertisers”) periodically, at pseudo-random intervals, pass advertising packets which the master device (also known as scanner device, i.e., “scanner”) is scanning. Depending on the type of advertising packet sent by a slave device, the master device may respond to the received advertising packet by requesting a connection with the slave device, or may respond by requesting further information from the advertising device.
The BLE specification (Bluetooth Specification Versions 4.0, 4.1, 4.2) requires that individual BLE advertising packets be transmitted periodically from a BLE advertising device in advertising mode at T_advEvent intervals. T_advEvent consists of two components, advInterval which is a fixed time value, and advDelay which is a pseudorandom delay time for adding pseudorandom jitter of from 0 to 10 milliseconds. BLE advertising devices operating in advertisement mode in a Bluetooth mesh network environment use three different advertising channels (BLE channels 37, 38 and 39) to transmit advertisement (or advertising) data. Bluetooth mesh networks currently use advertising channels to transfer data, and interference from other network protocols, such as Wi-Fi or Zigbee protocols, may cause transmission errors in these channels. For compatibility reasons with Bluetooth enabled phones, Bluetooth mesh devices also support transferring data over Bluetooth connection.
A BLE advertising device typically transmits the same advertisement data on each advertising channel (BLE channels 37, 38 and 39) in a fixed sequence in an attempt to compensate for possible interference with one or more of the advertising channels from other wireless network protocols such as Wi-Fi and Zigbee. A BLE scanning device in the same network environment switches between the scanned advertising channels in a fixed sequence in order to scan packets on all advertising channels. In such a network environment, BLE devices scanning for transmitted advertisement packets do not know in advance on what channel and at what time an advertising device will transmit its next advertising packet.